Understanding the relationship between corn grain and forage yield is important
to dairymen and grain farmers who often contract with each other for corn silage
production. Recently, the grain versus forage relationship has set government Loan
Deficiency (LDP) Payments to farmers for corn silage acres.
The Relationship Between Corn Grain and Forage Yield: An Update
Joe Lauer, Corn Agronomist
Understanding the relationship between corn grain and forage yield is important
to dairymen and grain farmers who often contract with each other for corn silage
production. Recently, the grain versus forage relationship has set government Loan
Deficiency (LDP) Payments to farmers for corn silage acres.
Arriving at a fair and equitable price for corn silage is difficult due to the number
of factors involved that are dynamic and biologically variable. Factors include grain
yield, forage yield, production costs, grain price, harvesting costs, grain drying costs,
fertility value of stover, and forage quality (especially starch content and neutral
detergent fiber digestibility-NDFD).
Some growers will want to calculate the forage price based on corn grain yield (as
the alternative harvestable crop) and some dairymen will want to calculate the price
based on alternative forages (primarily alfalfa as the alternative forage source). In either
case, the final price is affected by supply and demand of corn grain within a region.
The objective of this paper objective is to describe the relationship between grain
and forage yield. For the growing seasons between 1997 and 2004, experiments were
conducted to measure the impact of hybrid plant density, planting date and row spacing
on corn performance. It is difficult to obtain data for both corn grain and forage yield as
usually one or the other is harvested in a field or research plot situation. In these studies,
harvest forage yield and quality was measured in four of eight rows in the plot. The
remaining four rows were left for later grain harvest yield and quality measurements.
The relationship between grain yield and forage yield
Grain yield treatment means ranged from 0 to 256 bushels per acre while dry
matter forage yields ranged from 3.0 to 12.3 tons dry matter per acre. The relationship
between grain yield and forage yield is shown in Figure 1. Little grain yield was
measured when forage yields were below 2 to 3 tons dry matter per acre. The relationship
between grain yield and forage yield was mostly linear through forage yields of 8 tons
dry matter per acre.
To calculate the value of an acre of corn silage, the amount of grain contained in
one ton of silage (grain equivalent) is multiplied by the corn price and the forage yield.
For example, if corn yielded 150 bushels/A and was 65% moisture, the grain equivalent
is 7.4 bushels of grain per ton of corn silage (Table 1). An average yield is 20.4 T/A. If
corn is priced at $2.00 per bushel, the value of the field is 7.4 bu/T x $2.00 /bu x 20.4
T/A = $302/A or $14.80 /T. Further negotiation would need to be conducted over harvest,
ensiling, and storage costs.
Factors that affect the grain equivalent calculation
Anything that affects grain or forage yield will affect grain equivalents contained
in corn forage. Depending upon grain yield level, grain yield equivalents per ton of corn
silage ranged from 3.3 to 7.4 bushels per ton of silage at 65% moisture. These values are
slightly higher than the values calculated by Jorgenson and Crowley in 1972.
The amount of moisture has a major influence on the relationship and needs to be
considered to accurately determine fair silage prices. Grain yield per ton of silage for four
moisture levels is shown in Table 1. For a field that yields 150 bu/A, the grain
equivalents range from 17.9 bu/T at 0% moisture to 6.3 bu/T at 70% moisture.
The growing environment affects the relationship between grain and forage yield.
Depending upon year, grain equivalents ranged from 6.4 to 9.4 at a 150 bu/A yield level
(Table 2). Due to the drought in 2005, many cornfields are shorter than normal but corn
yield appears to be high. If this observation holds true and grain yield is relatively greater
than forage yield, grain equivalents will be higher than normal.
In summary, the grain equivalents shown in Table 1 on average reflect the grain
versus forage yield relationship. Forage moisture and year significantly affect grain
equivalents and must be considered when negotiating a contract. Since the grain
equivalent calculation is so variable, we recommend in all cases, when buying corn silage
that the purchaser should chop corn as it is harvested to determine forage quality. Ideally,
contracts should be based on corn silage quality rather than grain equivalents.
